全文获取类型
收费全文 | 3168篇 |
免费 | 239篇 |
国内免费 | 39篇 |
出版年
2023年 | 22篇 |
2022年 | 43篇 |
2021年 | 91篇 |
2020年 | 51篇 |
2019年 | 70篇 |
2018年 | 98篇 |
2017年 | 114篇 |
2016年 | 145篇 |
2015年 | 176篇 |
2014年 | 168篇 |
2013年 | 243篇 |
2012年 | 270篇 |
2011年 | 208篇 |
2010年 | 166篇 |
2009年 | 139篇 |
2008年 | 150篇 |
2007年 | 139篇 |
2006年 | 117篇 |
2005年 | 85篇 |
2004年 | 107篇 |
2003年 | 91篇 |
2002年 | 90篇 |
2001年 | 54篇 |
2000年 | 62篇 |
1999年 | 45篇 |
1998年 | 26篇 |
1997年 | 24篇 |
1996年 | 33篇 |
1995年 | 22篇 |
1994年 | 15篇 |
1993年 | 15篇 |
1992年 | 18篇 |
1991年 | 20篇 |
1990年 | 16篇 |
1989年 | 12篇 |
1988年 | 20篇 |
1987年 | 17篇 |
1986年 | 8篇 |
1985年 | 26篇 |
1984年 | 10篇 |
1983年 | 14篇 |
1982年 | 18篇 |
1981年 | 21篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1975年 | 10篇 |
1974年 | 8篇 |
1973年 | 13篇 |
排序方式: 共有3446条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Biotechnological processes involving bacteria are strongly nonlinear. Therefore, both their productivity and the final product quality may be considerably improved by applying appropriate control strategies to modulate behavior of the bacteria during transitional states. This requires advance identification of indicative signals by off-line investigation (i.e. experimental analysis) and on-line monitoring, (i.e. real time evaluation). A modular scheme is presented for doing this, which incorporates an Extended Kalman Filter and a prediction filter. If this is based on a suitable process-feature vector, which must be chosen in advance, the system can provide sufficient information to trigger appropriate feedback signals. Thus, it can provide a key element in modular situation control, allowing continuously periodic process management. In this publication the individual modules involved, and their assembly into an integrated system are described. Potential problems concerning selection of the feature vector, and experimental results are also discussed. 相似文献
5.
Molecular Genetics and Genomics - 相似文献
6.
John A. Nyakatura Vivian R. Allen Jonas Laustr?er Amir Andikfar Marek Danczak Hans-Jürgen Ullrich Werner Hufenbach Thomas Martens Martin S. Fischer 《PloS one》2015,10(9)
Orobates pabsti, a basal diadectid from the lower Permian, is a key fossil for the understanding of early amniote evolution. Quantitative analysis of anatomical information suffers from fragmentation of fossil bones, plastic deformation due to diagenetic processes and fragile preservation within surrounding rock matrix, preventing further biomechanical investigation. Here we describe the steps taken to digitally reconstruct MNG 10181, the holotype specimen of Orobates pabsti, and subsequently use the digital reconstruction to assess body mass, position of the centre of mass in individual segments as well as the whole animal, and study joint mobility in the shoulder and hip joints. The shape of most fossil bone fragments could be recovered from micro-focus computed tomography scans. This also revealed structures that were hitherto hidden within the rock matrix. However, parts of the axial skeleton had to be modelled using relevant isolated bones from the same locality as templates. Based on the digital fossil, mass of MNG 10181 was estimated using a model of body shape that was varied within a plausible range to account for uncertainties of the dimension. In the mean estimate model the specimen had an estimated mass of circa 4 kg. Varying of the mass distribution amongst body segments further revealed that Orobates carried most of its weight on the hind limbs. Mostly unrestricted joint morphology further suggested that MNG 10181 was able to effectively generate propulsion with the pelvic limbs. The digital reconstruction is made available for future biomechanical studies. 相似文献
7.
8.
Lydie M. Dupont Hans Peter Linder Florian Rommerskirchen Enno Schefuß 《Journal of Biogeography》2011,38(6):1059-1068
Aim To test whether the radiation of the extremely rich Cape flora is correlated with marine‐driven climate change. Location Middle to Late Miocene in the south‐east Atlantic and the Benguela Upwelling System (BUS) off the west coast of South Africa. Methods We studied the palynology of the thoroughly dated Middle to Late Miocene sediments of Ocean Drilling Program (ODP) Site 1085 retrieved from the Atlantic off the mouth of the Orange River. Both marine upwelling and terrestrial input are recorded at this site, which allows a direct correlation between changes in the terrestrial flora and the marine BUS in the south‐east Atlantic. Results Pollen types from plants of tropical affinity disappeared, and those from the Cape flora gradually increased, between 10 and 6 Ma. Our data corroborate the inferred dating of the diversification in Aizoaceae c. 8 Ma. Main conclusions Inferred vegetation changes for the Late Miocene south‐western African coast are the disappearance of Podocarpus‐dominated Afromontane forests, and a change in the vegetation of the coastal plain from tropical grassland and thicket to semi‐arid succulent vegetation. These changes are indicative of an increased summer drought, and are in step with the development of the southern BUS. They pre‐date the Pliocene uplift of the East African escarpment, suggesting that this did not play a role in stimulating vegetation change. Some Fynbos elements were present throughout the recorded period (from 11 Ma), suggesting that at least some elements of this vegetation were already in place during the onset of the BUS. This is consistent with a marine‐driven climate change in south‐western Africa triggering substantial radiation in the terrestrial flora, especially in the Aizoaceae. 相似文献
9.
Curt Koßwig 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1932,4(1):22-32
Ohne Zusammenfassung 相似文献
10.